1. Field of the Invention
The present invention relates to an image forming apparatus, such as a digital copying machine or a laser printer, and an optical scanning device used in the image forming apparatus.
2. Description of the Related Art
There is a known image forming apparatus that scans a scanning surface by rotating a deflecting scanning means, such as a polygon mirror. As one of such image forming apparatuses, an image forming apparatus has been proposed that detects a rotation position of the deflecting scanning means, measures a time from output of a rotation position detection signal to first detection of a synchronous detection signal, stores the measured time, and after that, turns on a light source based on the stored time after the rotation position detection signal is detected (for example, see Japanese Patent Application Laid-open No. 11-218697).
Meanwhile, in a system that divides a light beam from one light source into two or more light beams and applies the light beams to opposing scanning optical systems to perform writing in a time-shared manner, an effective scanning periodic ratio is high. Therefore, a time interval from the end of an effective scanning area in one of the scanning optical systems to synchronous detection in the other one of the scanning optical systems is short. Therefore, when lighting of the light source is controlled based on the rotation position detection signal of the deflecting scanning means, unnecessary exposure may occur near the end of the scanning optical system opposite a synchronous detection section due to a position detection error of the rotation position detection signal.
The present invention has been made to solve the above problem, and an object thereof is to provide an optical scanning device and an image forming apparatus that, in a system that divides a light beam emitted by one light source into two or more light beams and applies the light beams to opposing scanning optical systems to perform writing in a time-shared manner, can prevent unnecessary exposure near the end of the scanning optical system opposing the synchronous detection section even when the rotation position detection signal of the deflecting scanning means contains a small position detection error.
Furthermore, another object of the present invention is to provide an optical scanning device and an image forming apparatus that can maximize a writable angular range as an effective scanning range and prevent an increase in the optical path length.